Liquid crystal display having wide viewing angle

ABSTRACT

Disclosed is a liquid crystal display comprising a first substrate; pixel electrodes formed on the first substrate, the pixel electrodes having formed thereon a first aperture pattern; a second substrate provided opposing the first substrate; a common electrode formed on the second substrate, the common electrode having formed thereon a second aperture pattern; liquid crystal material injected between the first and second substrates; and spacers provided between the first and second substrates for maintaining a predetermined gap between the first and second substrates, wherein center portions of the first aperture pattern and the second aperture pattern are substantially straight and formed alternatingly in parallel, and wherein the spacers are positioned at ends of the second aperture pattern.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display having a wideviewing angle, and more particularly, to a liquid crystal display inwhich a predetermined pattern is formed on common electrodes and pixelelectrodes to obtain a wide viewing angle.

(b) Description of the Related Art

A liquid crystal display (LCD) is structured having liquid crystalmaterial injected between an upper substrate, on which common electrodesand a color filter are formed, and a lower substrate, on which thin filmtransistors and pixel electrodes are formed. Voltages of differentpotentials are applied to the pixel electrodes and common electrodes toform an electric field, thereby varying the alignment of liquid crystalmolecules of the liquid crystal material. In this way, the transmittanceof incident light is controlled to enable the display of images.

In a vertically aligned (VA) LCD, long axes of the liquid crystalmolecules align themselves vertically to the substrates in a state whereno electric field is formed between the substrates. Accordingly, usingpolarizing plates, light is completely blocked when there is no electricfield. That is, in a normally black mode, since brightness of an offstate is extremely low, a higher contrast ratio than obtained in atwisted nematic LCD is realized.

When an electric field is formed, however, since the slanting directionof the liquid crystal molecules is irregular, there exist areas where apolarizing direction of polarizing plates of the upper and lowersubstrates corresponds to the direction of the long axes of the liquidcrystal molecules. In these areas, the liquid crystal molecules cannotrotate the polarizing direction of light such that the light is cut offby the polarizing plates. This results it dark areas on the screen,which is referred to as texture. Accordingly, it becomes necessary topattern the electrodes.

Further, permanent damage to brightness may occur in the verticallyaligned LCD if the display receives outside shock. That is, outsideshock to the LCD may significantly alter a thickness of a liquid crystalcell is significantly altered as a result of the elastic properties ofspacers used to maintain a cell gap between the substrates. Hence, thescreen becomes spotted.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to solve the aboveproblems.

It is an object of the present invention to provide a liquid crystaldisplay having a wide viewing angle, which improves picture quality andreduces brightness variations.

To achieve the above object, the present invention provides a liquidcrystal display comprising a first substrate, pixel electrodes formed onthe first substrate, and having a first aperture pattern, a secondsubstrate provided opposing the first substrate, a common electrodeformed on the second substrate having a second aperture pattern, liquidcrystal material injected between the first and second substrates, andspacers provided between the first and second substrates for maintaininga predetermined gap between the first and second substrates, whereincenter portions of the first aperture pattern and the second aperturepattern are substantially straight and formed alternatingly in parallel,and wherein the spacers are positioned at ends of the second aperturepattern.

According to a feature of the present invention, the first aperturepattern includes a first aperture formed in a first direction in anupper region of the pixel electrodes, and a second aperture formed in alower region of the pixel electrodes in a second direction, which formsa right angle with the first direction, and the second aperture patternincludes a first base aperture formed in the first direction at aposition corresponding to the upper region of the pixel electrodes, anda second base aperture formed in the second direction at a positioncorresponding to the lower region of the pixel electrodes.

According to another feature of the present invention, the firstdirection forms an oblique angle with edges of the pixel electrodes.

According to yet another feature of the present invention, the secondaperture pattern includes a first branch aperture that overlaps upperand lower edges of the pixel electrodes, and a second branch aperturethat overlaps left and right edges of the pixel electrodes the firstaperture pattern includes third apertures positioned at upper and lowercenter portions of the pixel electrodes uniformly provided with respectto the upper and lower edges of the pixel electrodes and the first andsecond aperture patterns divide the pixel electrodes into a plurality ofclosed polygonal shapes.

According to still yet another feature of the present invention, thesecond branch aperture than the base apertures.

According to still yet another feature of the present invention, thefirst direction is formed uniformly with one edge of the pixelelectrodes.

In another aspect, the present invention provides a liquid crystaldisplay comprising a first substrate pixel electrodes formed on thefirst substrate having a first aperture pattern, a second substrateprovided opposing the first substrate, a common electrode formed on thesecond substrate formed thereon a second aperture pattern, liquidcrystal material injected between the first and second substrates, andspacers provided between the first and second substrates for maintaininga predetermined gap between the first and second substrates, wherein thefirst aperture pattern includes a first aperture formed horizontallyfrom a first side of the pixel electrodes, and second and thirdapertures formed obliquely from the first aperture and symmetricallyabout the first aperture, and formed such that an interval between thesecond and third apertures decreases as a second side of the pixelelectrodes, which is opposite the first side, is approached, wherein thesecond aperture pattern includes (a) a base portion formed horizontally,(b) a fourth aperture having first and second branches formed obliquelyfrom the base portion such that a distance between the first and secondbranches increases in a direction away from the base portion, and havingfirst and second branch ends formed vertically in opposite directionsfrom distal ends respectively of the first and second branches, (c) afifth aperture having a first center portion formed substantially inparallel with the first branch, and having first and second bendsforming horizontal and vertical portions, and (d) a sixth apertureformed symmetrically with the fifth aperture about the fourth aperture,wherein the first and second aperture patterns are formed alternatinglywhen the liquid crystal display is viewed from above, and wherein thespacers are provided at ends of the second aperture pattern.

In yet another aspect, the present invention provides a liquid crystaldisplay comprising a first substrate, pixel electrodes formed on thefirst substrate having a first aperture pattern, a second substrateprovided opposing the first substrate, a common electrode formed on thesecond substrate having a second aperture pattern, and liquid crystalmaterial injected between the first and second substrates, wherein thefirst aperture pattern includes first apertures dividing an upperportion of the pixel electrodes into vertical regions, and secondapertures formed below the first apertures to divide a lower portion ofthe pixel electrodes into horizontal regions, wherein the secondaperture pattern includes third apertures formed vertically, and fourthapertures formed horizontally below the third apertures, and wherein thefirst apertures and the third apertures are alternatingly formed todivide the upper portion of the pixel electrodes into a plurality ofregions, and the second apertures and fourth apertures are alternatinglyformed to divide the lower portion of the pixel electrodes into aplurality of regions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention.

FIG. 1 is a schematic sectional view of a portion of a liquid crystaldisplay according to a preferred embodiment of the present invention.

FIGS. 2 and 3 are schematic plan views of an aperture pattern formed onupper and lower substrates of an LCD, and spacers provided between thesubstrates, according to first and second preferred embodiments,respectively, of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

FIG. 1 shows a schematic sectional view of a portion of a liquid crystaldisplay according to a preferred embodiment of the present invention.

The liquid crystal display includes a first (lower) substrate 10 and asecond (upper) substrate 20, which are provided substantially inparallel with a predetermined gap therebetween, a liquid crystal layer310 formed of liquid crystal material between the substrates 10 and 20,and comprised of liquid crystal molecules 30 that are alignedperpendicular to the substrates 10 and 20, and spacers 100 providedbetween the substrates 10 and 20, the spacers 100 maintaining apredetermined gap between the substrates 10 and 20.

Pixel electrodes 12 are formed on the first substrate 10, the firstsubstrate 10 being made of a transparent insulating material. The pixelelectrodes 12 are made of a transparent conducting material such as ITO(indium tin oxide) or IZO (indium zinc oxide), and have an aperturepattern (not shown) formed thereon. Each pixel electrode 12 is connectedto a switching element 11 to receive an image signal voltage. A thinfilm transistor is generally used for the switching elements 11. Eachthin film transistor is connected to a gate line (not shown), whichtransmits scanning signals, and to a data line (not shown), whichtransmits image signals. The thin film transistors turn the pixelelectrodes 12 on and off according to the scanning signals. Further, anorientation layer 15 for orienting the liquid crystal molecules 30 isalso formed on the first substrate 10. Finally, a lower polarizing plate14 is provided on an outer surface of the first substrate 10. In areflective-type LCD, it is not necessary that the pixel electrodes 12 bemade of a transparent material, nor is it necessary to attach the lowerpolarizing plate 14 to the first substrate 10.

Formed on the second substrate 20, which is made of a transparentinsulating material like the first substrate 10, are a black matrix 21for preventing light leakage; a red, green, blue color filter 22 acommon electrode 23 made of a transparent conducting material such asITO and IZO, and having an aperture pattern (not shown) formed thereon;and an orientation layer 25 for orienting the liquid crystal moleculesof the liquid crystal layer 310. It is possible for the black matrix 21or the color filter 22 to be formed on the first substrate. There isalso provided an upper polarizing plate 24 on an outer surface of thesecond substrate 20.

The lower and upper polarizing plates 14 and 24 are arranged such thattheir polarizing directions are perpendicular to each other in thenormally black mode, and in the normally white mode, the polarizingdirections are parallel. The following description will be about thenormally black mode.

FIG. 2 shows a schematic plan view of an aperture pattern formed onfirst and second substrates, and spacers provided between thesubstrates, according to a first preferred embodiment of the presentinvention. The drawing depicts the substrates in a combined state, thatis, in a state where the second substrate is provided opposing the firstsubstrate with a predetermined gap therebetween.

Formed on the first substrate is gate wiring, which includes gate lines202 for transmitting scanning signals and gate signals, and gateelectrodes 204 of thin film transistors, which are connected to the gatelines 202. Also formed on the first substrate is data wiring. The datawiring includes data lines 62 intersecting the gate lines 202 to defineunit pixels, the data lines 62 transmitting data signals; sourceelectrodes 65 of the thin film transistors, which are connected to thedata lines 62; and drain electrodes 66 of the thin film transistors,which oppose the source electrodes 65 centered about the gate electrodes204. Here, the pixel electrodes 12 and the drain electrodes 66 areelectrically connected such that the pixel electrodes 12 receive datasignals from the data wiring 62, 65 and 66. Further, storage wiring 27and 28 is formed on a circumference of the unit pixels, the storagewiring 27 and 28 overlapping the pixel electrodes 12 to form a storagecapacitance, and preventing the leakage of light through the edges ofthe unit pixel.

A first aperture 121 is formed in each pixel electrode 12. The firstapertures 121 penetrate through a center portion of the pixel electrodes12 starting from a right side thereof (in the drawing), and extendalmost the entire width of the pixel electrodes 12 to divide the pixelelectrodes 12 into an upper half and a lower half. The first apertures121 are wide where they begin (their “openings”) on the right side ofthe pixel electrodes 12 then taper at two different predetermined anglesto a predetermined width, after which the first apertures 121 continueat this width for the remainder of their length Further, second andthird apertures 122 and 123 are formed respectively in the upper andlower half of each pixel electrode 12. The second and third apertures122 and 123 are symmetrical about the first apertures 121, and areformed starting from the right side of the pixel electrodes 12 andextend to a left side (in the drawing) of the same at a predeterminedangle. The left sides of the pixel electrodes 12 where the second andthird apertures 122 and 123 end are protruded outwardly to preventconnection defects caused by the second and third apertures 122 and 123.

A fourth aperture is formed in each unit pixel of the common electrode23, which is continuously formed over an entire surface of the secondsubstrate. The fourth aperture includes an apex 211 formed in ahorizontal direction (in the drawing), first and second branches 212 and214 obliquely formed from the apex 211 extending respectively upwardlyand downwardly, and first and second branch ends 213 and 215 extendingvertically from distal ends of the first and second branches 212 and214. Further, a fifth aperture is formed above (in the drawing) thefourth apertures. The fifth apertures include a center portion 221extending from one edge of the unit pixel to an adjacent edge at anangle identical to the first branch 212, a horizontal portion 222extending in the horizontal direction from the center portion 221, and avertical portion 223 extending in the vertical direction from the centerportion 221. Sixth apertures including center, horizontal and verticalportions 231, 232 and 233 are formed symmetrically with the fifthapertures on the opposite side of the fourth apertures. The fourth,fifth and sixth apertures are formed in the same manner in each unitpixel of the common electrode 23.

As shown in FIG. 2, portions of the first, second and third apertures121, 122 and 123 of the pixel electrodes 12 overlap portions of thefourth, fifth and sixth apertures of the common electrode 23 to dividethe pixel electrode into a plurality of regions. The center portion 221of the fifth aperture, the second aperture 122, the first branch 212 ofthe fourth aperture, the second branch 214 of the fourth aperture, thethird aperture 123, and the center portion 231 of the sixth aperture areprovided in parallel in an alternating manner.

As a result of the above aperture configuration, the liquid crystalmolecules, which are re-aligned following the formation of an electricfield between the substrates, are slanted in four different directionsin each pixel region according to the fringe field formed as a result ofthe apertures.

Provided at ends of the elements 211, 213, 215, 222, 232 and 233 of theapertures of the common electrode 23 are spacers 100. The spacers aremade of an organic material and act to maintain a uniform gap betweenthe substrates. With this configuration, directors of the liquid crystalmolecules at ends of the elements 211, 213, 215, 222, 232 and 233 of theapertures are not aligned in various directions preventing disclination.That is, when a drive voltage is applied to the pixel electrodes 12 andthe common electrode 23 to control the liquid crystal molecules, theelectric field at ends of the elements 211, 213, 215, 222, 232 and 233is not uniformly formed and a slanting of the electric fieldsignificantly varies. This causes the non-uniform alignment of theliquid crystal molecules. By providing the organic spacers 100 at theselocations, disclination is prevented. In addition, the spacers 100 areable to securely maintain the gap between the substrates even whenoutside shocks are applied to the LCD, in which prevents brightnessreduction caused by changes in the gap.

The above aperture patterns can take various shapes to dividedly alignthe liquid crystal molecules. However, it is preferable that thefollowing conditions be satisfied.

(i) It is preferable that a single pixel region is divided into four inorder to realize a wide viewing angle.

(ii) In order to realize a stable divided alignment of the liquidcrystal molecules, neither disclination nor texture should occur outsidethe borders of the divided small regions. With disclination, thedirectors of the liquid crystal molecules may assume various directionsrather than a uniform direction in a small region. Hence, the liquidcrystals are slanted so that they contact one another in a single pixelregion. It is therefore preferable that the patterns of the first andsecond substrates are repeated to realize a stable divided alignment,and that the patterns of the first and second substrates are formed asclose together as possible. Stated differently, when viewing theapertures in a combined state from above (top sectional view), it ispreferable that the regions formed by the patterns of the first andsecond substrates assume closed polygonal shapes. Further, sincedisclination can easily occur if an acute angle is formed in thepatterns to define one region, it is preferable that only obtuse anglesbe formed in the patterns. A stable divided alignment is also necessaryto obtain good brightness characteristics. In a region with a scatteredalignment, light appears brighter in an off state and some portions aredarker than other portions result in an on state. The scatteredalignment regions change location during liquid crystal moleculealignment and generate afterimages.

(iii) This following condition must be satisfied in order to obtain ahigh brightness. First, it is preferable that the liquid crystaldirectors of adjacent regions meet each other at 90 degree angle. Bymeeting this criterion, disclination occurs only at the narrowestregion. Also, an angle between a transmission axis of the polarizingplate and the liquid crystal directors is 45 degrees can achieve thehighest brightness. Further, it is preferable that bending or angling ofthe angles made by the apertures of the first and second substrates bereduced as much as possible.

(iv) To obtain a good response speed, the above condition to betterobtain brightness by minimizing bending or angling of the angles made bythe apertures of the first and second substrates must be satisfied.

FIG. 3 shows a schematic plan view of an aperture pattern formed onfirst and second substrates, and spacers provided between thesubstrates, according to a second preferred embodiment of the presentinvention. The drawing depicts the substrates in a combined state, thatis, in a state where the second substrate is provided opposing the firstsubstrate with a predetermined gap therebetween.

Storage wiring 27, 28 and 29 occupies edges of unit pixels and is formedcorresponding to an aperture pattern of the pixel electrodes 12. Theaperture pattern of the pixel electrodes 12 includes a first aperture111 that divides an upper portion (in the drawing) of the pixelelectrodes 12 into left and right (in the drawing) halves, and a secondaperture 120 that divides a lower portion (in the drawing) of the pixelelectrodes 12 into four portions. Further, a third aperture is formed inthe common electrode 23 of each unit pixel. The third aperture includesa horizontal portion 230 formed substantially in a center area of eachpixel region to divide the common electrode 23 of a unit pixel intoupper and lower portions (in the drawing), and first and second verticalportions 210 and 220 extending from the horizontal portion 230 acrossthe upper portion of the common electrode 23 of a unit pixel. Formedhorizontally (in the drawing) in the lower portion of the commonelectrode 23 of a unit pixel are fourth and fifth apertures 240 and 250.Unconnected ends of the elements 210, 220, 230, 240 and 250 expand intotriangular shapes.

As shown in FIG. 3, the first aperture 111 of the pixel electrodes 12and the first and second vertical portions 210 and 220 of the commonelectrode 23 in each unit pixel are alternatingly formed in parallelsuch that the upper portions of the pixel electrodes 12 are divided intofour substantially equal vertical regions. Further, the second apertures120, the horizontal portion 230 of the third aperture, the fourthaperture 240, and the fifth aperture 250 are alternatingly formed inparallel in a horizontal direction starting from the center of the pixelregions and extending downward to the lower portion of the pixelregions. Accordingly, the pixel electrodes 12 are divided into sixsubstantially equal regions.

In addition, provided at ends of the elements 210, 220, 230, 240 and 250of the apertures of the common electrode 23 are spacers 100. The spacers100 are made of an organic material, act to maintain a uniform gapbetween the substrates, and otherwise provide the same benefits asoutlined with respect to the first preferred embodiment.

Although preferred embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

For example, although aperture patterns are formed in the commonelectrode and the pixel electrodes in the above embodiments, it ispossible to form both an aperture pattern and protrusions only in thepixel electrodes. In this case, the protrusions can be formed, forexample, out of the gate insulating layer or the protection layer. Whenprotrusions are formed, care must be taken to prevent the parasiticcapacitance in the spaces between the wiring. As another example, anaperture pattern may be formed in the pixel electrodes and protrusionsin the common electrode.

1. A liquid crystal display, comprising: a first substrate; pixelelectrodes formed on the first substrate and having a first aperturepattern; a second substrate provided opposing the first substrate; acommon electrode formed on the second substrate and having a secondaperture pattern; liquid crystal material injected between the firstsubstrate and the second substrate; and spacers provided between thefirst substrate and the second substrate for maintaining a predeterminedgap between the first substrate and the second substrate, wherein centerportions of the first aperture pattern and the second aperture patternare substantially straight and formed alternatingly in parallel, andwherein the spacers are positioned at ends of the second aperturepattern.